I run C1 4.8.2 DB on a four-year-old G5 powermac with 10.5.8. When C1 opens, a dialog box tells me the G5 is not compatible, but I press "continue" and everything goes smoothly. It may be a bit slow, but I have never had any glitch or problem.

Just to share another person's experience: I had NO problems with C1 Pro v4.1.1x on a rev. A PowerMac G5 (dual processor) running OS 10.4.11. It is not "zippy" when using this config. but serviceable. Don't try to open PS while C1 is open if using this approach as C1 seems to gag on it. I don't know about C1 4.8x as I didn't try it.